Typically, glass fibers are formed by drawing molten glass into filaments through a bushing or orifice plate and applying an aqueous sizing composition containing lubricants, coupling agents, and film-forming binder resins to the filaments. The sizing composition provides protection to the fibers from interfilament abrasion and promotes compatibility between the glass fibers and the matrix in which the glass fibers are to be used. After the sizing composition is applied, the wet filaments may be gathered into one or more strands, chopped, and collected. The chopped strands may contain hundreds or thousands of individual glass fibers. The collected chopped glass strands may then be packaged in their wet condition as wet use chopped strands (WUCS) or dried to form dry use chopped strands (DUCS).
Wet chopped strands are conventionally used in wet-laid processes in which the wet chopped fibers forming the wet chopped strands are dispersed in a water slurry that contains surfactants, viscosity modifiers, defoaming agents, and/or other chemical agents. The slurry containing the chopped fibers is then agitated so that the fibers become dispersed throughout the slurry. The slurry containing the fibers is deposited onto a moving screen where a substantial portion of the water is removed to form a web. A binder is applied, and the resulting mat is dried to remove any remaining water and cure the binder. The formed non-woven mat is an assembly of dispersed, individual glass fibers.
Fibrous mats formed by wet-laid processes are extremely suitable as reinforcements for many types of applications. For example, wet-laid mats may be used in roofing applications, non-woven veil applications, or to form composite laminates or ceiling tiles. Because the fibers are not dried prior to use, wet-laid mats provide a lower cost alternative to dry-laid mats. Besides their economic advantage, wet-laid mats have the attributes of good wettability for impregnation by plastic resins, quick air releasing capacity, and superior surface characteristics. In addition, they serve well as spacing and core material.
Although wet-laid mats possess many desirable attributes, attempts are continually being made to improve conventional chopped strand mats. One particular area of interest is improving the tear and tensile strengths of the mats, as these properties are consumer-oriented and consumer-driven. Some examples of attempts to improve chopped strand mats are set forth below.
U.S. Pat. No. 6,179,962 to Brady, et al. discloses a process for making paper that adds the combination of a water soluble and/or water dispersible cationic polymer and an oxidized galactose type of alcohol configuration containing polymer to the pulp water. The oxidized galactose type of alcohol configuration may contain polymers such as neutral, anionic, and/or amphoteric oxidized guar. Oxidized guar is preferred as the oxidized galactose type of alcohol. It is asserted that the water soluble and/or water dispersible cationic polymer and the oxidized galactose type of alcohol configuration containing polymer can be added at anywhere in the process of papermaking, including the white water chest. The process is asserted to improve the paper strength.
U.S. Pat. No. 6,642,299 to Wertz, et al. teaches an adhesive aqueous binder composition that contains a urea-formaldehyde resin modified with an additive that includes (1) styrene acrylic acid or styrene acrylate, (2) an adduct of styrene, maleic anhydride, and an acrylic acid or acrylate, or (3) a physical mixture of a styrene-maleic anhydride copolymer. The adduct can be preformed and then added to the urea-formaldehyde resin, or it can be formed in situ in the binder resin by blending, with the urea-formaldehyde resin, a physical mixture of styrene-maleic anhydride and an acrylate monomer. The modified binder is used to prepare fiber mats that assertedly have improved wet and dry tensile properties. The mats may be formed by a white water process.
Although conventional wet-laid mats are continually being improved, there remains a need in the art for a method for improving the tear strength of chopped strand mats, especially during the manufacture of the chopped strand mats.